The present invention relates to a motor apparatus that may be used for blower motors in vehicular air conditioner systems.
Outer rotor-type brushless motors are used as blower motors for vehicular air conditioners. In this type of motors, a rotor vibrates while in operation. It is proposed in JP-A-11-289735 published on Oct. 19, 1999 to minimize this vibration by fixing bosses of a fixing plate to a casing via vibration-restricting cushions. In the case of three-phase full-wave six-pole motor, for instance, the vibrations arise from magnetic variation generated when a stator coil passes permanent magnets. This vibration results in the eighteenth-order vibration component (18f) that occurs eighteen times per rotation of the rotor. The vibration also arises when the rotor rotates with its rotary axis being inclined from its normal rotation axis. This inclined rotary motion is caused from weight imbalance of the rotor including a fan fixed at one end of a rotor shaft. This vibration results in the first-order vibration component (1f) that occurs once per rotation of the rotor.
As indicated by a curve S in FIG. 6, the vibration transmission rate of the eighteenth-order vibration component (18f) is low but the rate of the first-order vibration component (1f) is high, if the cushion is made of a low hardness material (soft material). Thus, the vibration arising from the weight imbalance cannot be sufficiently reduced, although the vibration arising from the magnetic variation can be sufficiently reduced. On the contrary, as indicated by a curve H, the vibration transmission rate of the first-order vibration component (1f) and the rate of the eighteenth-order vibration component (18f) are generally the same, if the cushion is made of a high hardness material (hard material H). Thus, both of the vibrations arising from the magnetic variation and arising from the weight imbalance cannot be sufficiently reduced.
It is an object of the present invention to provide a motor apparatus that is less vibrant against magnetic variation and weight imbalance of a rotor.
According to the present invention, a motor apparatus comprises a motor holder formed with a plurality of fixing holes, a stator having a fixing plate, a rotor rotatably supported by the stator, and a cushion interposed between the motor holder and the fixing plate.
In one aspect of the invention, the cushion is formed in generally a cylindrical shape to have an abutting surface on an inner peripheral surface for abutment with an outer peripheral surface of a boss formed integrally with the fixing plate or a fixing member. The cushion is formed to have an annular groove on an outer peripheral surface for engagement with the motor holder. The inner abutting surface has an axial length shorter than an entire axial length of the cushion.
In another aspect of the invention, the cushion is divided into a first cushion and a second cushion, and the fixing holes are divided into a first fixing hole and a second fixing hole. A boss of the fixing plate or a fixing member is fit in the first cushion fit in the first fixing hole. No boss nor fixing member is fit in the second cushion fit in the second fixing hole. The first cushion and the second cushion are fixedly held to the fixing plate by a holding plate in an axial direction.
Preferably, each of the fixing holes is formed in an elongated shape in a circumferential direction so that the cushion is deformed to provide a small spring constant in a rotation direction of the rotor.